The transient inhibition by xylitol of strains of L. casei growing at the expense of ribitol appears to be the result of a xylitol-driven futile cycle. Growth studies and resting cell experiments demonstrated that L. casei Cl-16 possesses the ability to (1) import xylitol via a specific phosphotransferase system (PTS), (2) dephosphorylate the transport product xylitol-5-P to xylitol and (3) export free xylitol. These enzymatic activities provide the cell with all of the components required to drive a cycle that pumps xylitol into and out of the cell. Since this mechanism requires PEP, its operation depletes the cells' energy supplies. It is this depletion of the energy reserves that accounts for the inhibition in growth, however, sufficient energy remains to permit maintenance functions. Thus, the inhibition is only bacteriostatic in nature rather than bacteriocidal. The coaggregation of Cytophaga sp. DR 2001 and Actinomyces isrealii appears to be mediated by a lectin-like protein component of the outer membrane of the cytophaga. Analysis by SDS-PAGE electrophoresis, western blot techniques and specifically absorbed antisera indicate that the lectin is an outer membrane protein (OMP) with a M.W. of 155,000 that is basic (anodal) in nature. Antisera are now being prepared against proteins suspected of lectin activity. Efforts to isolate the carbohydrate receptor from A. israelii cell walls using specific plant lectins are also underway.